No Measurable High Pressure GM A6 Replacement

[1GCamaro]

New Member here with a very strange situation. Expert advice appreciated.

It gets more interesting - so please read it all. Surprise ending, even.

I've replaced my A6 factory compressor on my '67 Camaro 327, along with all components except for evap and condenser and muffler. When it was open I flushed the entire system with solvent, then with air. Car had previously been switched to R134a. I did install the appropriate PAG 150 oil. (Confirmed amount)

I vacuumed it down with no problem. High side gauge drops into negative territory and Low Side drops almost to -30. So far, so good.

Begin installing R134 as normal, and I see Low side readings around 20 - 30. With the POA Valve upgrade it is necessary to connect the POA switch to get the compressor going at this stage. After the first can of R134 flows in, I see no High side pressure at all. This is strange, as we'd expect to see something at this point. Beginning the second can of R134, the compressor clutch starts screeching! Shut down the compressor and let things rest a moment. Still no High pressure. It is still in the negative as when it was vacuumed! Yes, it's not Zero. It is still negative! (Red valve on gauge remains closed always)

Turn compressor back on, and in about 10 seconds I get the screeching clutch. As a test, I remove the jumper on the POA switch to let the compressor attempt to operate normally. Still attempting the second can at this time. Well, as you may expect, the negative pressure rises and falls rapidly, with the POA switch doing its thing, cycling the comp on and off very quickly! Every 2 seconds or so we see the Low side pressure change, which of course causes the comp cycling. As the cycling occurs, we get an occasional momentary screech. When comp turns on, negative pressure drops to near zero, but jumps to around 50 - 60 when pressure switch opens. Cycles continuously.

Still no High pressure measured. Still in Negative! Quick observation makes us think compressor is pulling negative on the Low side and nothing happening on the High side. I then talked with the SMP guys in TX - and their expert said there had to be some sort of restriction in the system - or a defective compressor. I am baffled that even with a restriction, wouldn't I see some high side pressure since the muffler and port is connected right there to the High side of the compressor?

But no - the High gauge still reads below Zero! And Low Side static pressure is 120psi at this point. I opened the low side to relieve the pressure before taking next step. Note: After low side is bled to zero, high side gauge still below zero. The next item is the surprise ending.

Next step: Check compressor port connector for blockage or whatever. Remove the block-type connector which opens both sides of compressor. Nothing unusual found. High side gauge still showing negative, even with compressor port connector wide open. Huh? Is there a blockage in the muffler? Inserting a flexible plastic probe allows me to go all the way through the muffler and into the hose going to condenser. No blockage. Gauge still shows negative.

Open high side port at the gauge set and the negative reading disappears as the vacuum (still present up to that point) dissipates. What's in that muffler? A valve in addition to the Schrader? Something else blocking port access inside muffler?

Why no High pressure at all? Why the continuous negative reading while R134 was added and compressor running? Why compressor clutch screech? I'd have to guess the clutch screech is a result of comp attempting and being blocked by super-high internal pressure? Can't let that happen long or clutch burns up and/or compressor too. Only a couple seconds.

First possibility was gauge set not opening Schrader in muffler, but no that's not the problem. Still uncertain what's going on, but one thing that seems obvious is that the high side port is not showing what's going on in the high pressure line between the compressor and the condenser. Vacuum down again, and when we put half a can of R134 in, the pressure switch begins to cycle - with the pressure dropping to zero when the compressor kicks on for one second -- then up to around 50pis when the compressor is off. This behavior repeats continuously, and we still have no high side reading at all. When the engine is shut down and things go into steady-state, we see pressure on the low side but none on the high side. But if we do nothing for two hours we begin to see some static pressure on the high side. Is there some sort of blockage between the port and the main line in the muffler? Get this: When we reach steady state and finally see some pressure on the high side port, we can disconnect the compressor port hoses and of course the low side pressure drops - but the high side pressure does not! This again makes us think there's something terrible wrong in the muffler. Reading some static pressure on the High side when system is open! Open red hose to gauge, it drops -- reconnect hose to gauge and it very slowly builds.

Help!!

[JohnHere]

Is the replacement A-6 new or rebuilt? I ask because it sounds like a compressor problem to me...possibly the valves being incorrectly assembled during a rebuild, causing compressor lock-up and the accompanying clutch squeal.

From what you said, it sounds like the system is running a POA eliminator, too. I don't recommend installing those because the A-6 is designed to run continuously and not to cycle. Cycling the A-6 will result in a ruined clutch before long and might shorten the life of the compressor as well.

[1GCamaro]

Is the replacement A-6 new or rebuilt? I ask because it sounds like a compressor problem to me...possibly the valves being incorrectly assembled during a rebuild, causing compressor lock-up and the accompanying clutch squeal.

From what you said, it sounds like the system is running a POA eliminator, too. I don't recommend installing those because the A-6 is designed to run continuously and not to cycle. Cycling the A-6 will result in a ruined clutch before long and might shorten the life of the compressor as well.

Thanks for the reply. It is a rebuilt A-6, and the SMP guys insist these are rigorously tested before shipping. But it could indeed be a bad one.

It is indeed the POA eliminator. My old POA was stuck open and I didn't pursue getting a real replacement. The car isn't driven much and won't be run through a huge number of cycles. If it was my daily driver I'd go back to POA so the A-6 wouldn't cycle.

Despite what's going on the with compressor, the action of the muffler and high port is still quite confusing.

[1GCamaro]

Is the replacement A-6 new or rebuilt? I ask because it sounds like a compressor problem to me...possibly the valves being incorrectly assembled during a rebuild, causing compressor lock-up and the accompanying clutch squeal.

From what you said, it sounds like the system is running a POA eliminator, too. I don't recommend installing those because the A-6 is designed to run continuously and not to cycle. Cycling the A-6 will result in a ruined clutch before long and might shorten the life of the compressor as well.

I removed the rebuilt compressor and wanted to measure the amount of oil still in it so I'd know how much to add to the replacement comp before installing it. I opened the sump plug and none at all came out. None! The connector ports were also open to be sure there's air flow. Shouldn't I see some oil remaining in this - or is there some sort of backflow valve in there that prevents oil from flowing out the plug? That's obviously the same plug I opened to insert the oil. Where'd it go? Is it all distributed throughout the system, but none remaining in the comp since there's something wrong with it?

Did I vacuum the oil out? I did have a small amount of oil under the vacuum pump, but figure that was from the pump. But everything I've read says pump will not take the oil out of the system.

I'm going to install another compressor, but unless I flush the entire system again I'll have no real proof of the amount of oil in there. I'd rather not try and operate with too much oil. What would y'all do?

[1GCamaro]

In case anyone is following this saga, I opened the system up and did another full flush.

(1) Condenser was bone dry. Nothing but air. Flushed with solvent anyway, then lots more air.
(2) Evap was loaded with oil! Flushed it all out. Did the oil in the compressor all get pulled into the evap? How?

Ideas?

[JohnHere]

It has been a long time, but if memory serves, the A-6 holds about 10 ounces of oil in its sump and should always contain "some" oil for proper lubrication. By some, I'm thinking around 8 ounces because an ounce or two normally will circulate with the refrigerant...and be retained in...the condenser, evaporator, and receiver/dryer or accumulator.

Why the evaporator in your Camaro was full of oil while the compressor had none I can't say. But I still suspect a problem with the valving in the rebuilt A-6, or something else internally, that caused the lack of high-side pressure, all the oil to be pumped out, and the apparent compressor lock-up.

Incidentally, was there any oil in the compressor when you purchased it?

[1GCamaro]

The info that comes with the compressor says it is pre-charged with 3 ounces of oil -- (system needs 11 oz total) and that the installer should add half the remainder to the compressor ahead of install -- then put the remainder in with the refrigerant. I added 4 oz to the compressor before installing, then added the final 4 oz. I have read elsewhere that the A6 holds all the oil in the sump, but the instructions don't say to put it all in there at the start. The docs also say to rotate the comp by hand a dozen times before cranking up the engine in order to get some or most of the oil out of the valves and beginning to be distributed through the system.

In my case I'm baffled wondering if the comp pumped OK at first and shoved all the oil thru the condenser and up into the evaporator -- or maybe my vacuuming could have sucked it out of the comp into the evap? I'm also still confused by the strange action of the muffler and will re-test that before attempting to start charging again. I want to see if I'll find the high side valve port still holds/shows negative pressure when the manifold is disconnected from the compressor.

[sonoraed]

sometimes this problem is caused by guage set, this can be diagnosed if still in vacuum by static charging thru high side (with engine off) refrigerant should go thru high side and low side guage will rise, another way to tell if guage set ok would be when system is in a vacuum loosen low side hose at guage set , high side should rise to atmospheric pressure, if not I would say blockage in system, is there a possibility AC suction/discharge reversed at compressor?
Please post solution when you find it

[tbirdtbird]

Unrelated to your problem, probably, but personally I would have eliminated the muffler, just one more thing to go wrong

[1GCamaro]

Unrelated to your problem, probably, but personally I would have eliminated the muffler, just one more thing to go wrong

Only reason I've kept the muffler this long is that the high side port is on the muffler.